Regulating system



1943- H. M. RUSTEBAKKE ETAL 2,454,211

' REGULATING srsmu Filed maize. 1945 Frequency 60m pgnsuflnq Me'qnsPatented Nov. 16, 1948 REGULATING SYSTEM Bomer M. Rustebakke and AlbertWrKimball, Wilkinsburg, Pa., assignors to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of PennsylvaniaApplication November 29, 1945, Serial No. 631,724

4 Claims.. (Cl.'32277) This invention relates to regulating systems.

Regulating systems which utilize conventional exciters for controllingthe excitation of generators have been known for many years. Theconventional exciters are designed to have a saturation curve such thatsaturation starts at a point below the lowest normal operating point onthe curve in order to permit a stable manual control of the exciter.This is readily accomplished, for with a hand controlled rheostatadjusted in a predetermined manner and connected in the field circuit ofthe exciter, it is found that the resultant field circuit resistanceline provides a definite intersection at a'point along the excitersaturation curve and that the exciter voltage is at a valuecorresponding to the point of intersection. Such manual control isstable in that if the voltage of the exciter tends to rise, the increaseis insufilcient to produce enough field current to sustain the highervalue, whereas if the voltage tends to decrease, the field current ofthe exciter is excessive and functions to restore the voltage to a valuecorresponding to the point of intersection referred to hereinbefore.

Recently there has been developed a selfexcited or series tuned exciterwhich normally operates along the linear part of its saturation curve.Such exciters have a series field winding for normally supplying themajority of the excitation requirements with a shunt field for supplyingthe remainder of the excitation of the machine and at least one controlfield winding disposed to be directionally energized in response to theoperation of a generator, the excitation of which is controlled by theexciter. As the self-excited exciter operates on the linear part of itssaturation curve, it cannot be successfully manually controlled by arheostat in series with a shunt field but instead, if such a manualcontrol is utilized, it is found to be extremely unstable. This becomesevident when it is considered that the field circuit resistance line forthe self-excited exciter coincides with the air gap line of the exciterthroughout the linear part of the saturation curve, and that the samerheostat setting is required for all voltages from zero up to thesaturation point. Thus, as the voltage of the exciter tends to change,the field current changes the exciter is normally controlled by aregulator which is automatically responsive to changes in the voltage ofthe generator, it is essential that the manual control referred tohereinbefore be so disposed as to be utilized instead of the automaticregulator, as disclosed and claimed in copending application Serial No.631,726, filed November 29, 1945, in the names of E. L. Harder and C. E.Valentine. While the manual control circuit embodying the rectifier asdisclosed therein is satisfactory for normal operating conditions, it isfound that where the polarity of the exciter becomes reversed, themanual control of the Harder et al. application is incapable ofsatisfactorily controlling the excitation of the generator.

An object of this invention is to provide, in a regulating system whichutilizes a self-excited exciter for controlling the excitation of agenerator, for a manual control of the system while retaining theoperating characteristics of the exciter.

Another object of this invention is to provide in a regulating systemfor controlling the excitation of the generator for utilizing aself-excited exciter controlled by an interchangeable automatic andmanual control, the manual control being operative under'reversepolarity conditions of the exciter to control the operation of theexciter and thereby maintain the excitation of the generator.

A further object of this invention is to provide in a regulating systemwhich utilizes a selfexcited exciter for controlling the excitation of agenerator, for a manual control responsive to the output of the exciterand operative under reverse polarity conditions of the exciter tocontrol the operation of the exciter.

Other objects of this invention will become apparent from the followingdescription when taken in conjunction with they accompanying drawing inwhich the single figure is a diagrammatic representation of a regulatingsystem embodying the teachings of this invention.

Referring to the drawing, there is illustrated a generator ill, thevoltage of which is to be regulated. The generator it] comprises thearmature windings l2 and the field windings M, the armature windings i2being connected for supplying a three-phase load circuit represented byconductors l6, l8 and 20. The field windings H are connected to besupplied from a rotary czlirect-current generator or self-excitedexciter The self-excited exciter 22 schematically represente is of4-pole construction having a plurality o field windings and is of thegeneral construction and type disclosed and claimed in the copendingapplication, Serial No. 607,440, filed July 27, 1945, in the names of W.R. Harding and A. W. Kimball, and assigned to the assignee of thisinvention. As disclosed therein, the exciter or rotary direct-currentgenerator 22 has a number of pole pieces and an equal number ofcommutator brushes arranged to assume sequentially positive and negativeelectrical potentials. In the embodiment schematically shown in thedrawing, the positive brushes of the 4-pole machine are interconnectedby an equalizing connection as are also the negative brushes of themachine.

The exciter generator 22 is provided with forcing fields 23 and 24connected in series circuit relation in one of the equalizingconnections, the fields 23 and 24 being so' divided as to coristitutet'wogroupsof four windings each, a corresponding winding from eachgroupbeing arranged on each ofthe four poles to be equally and sequentiallyexcited by current flowing between the brushes. In addition to theforcing fields 23 and 24, the exciter generator 22 is also provided withcompensating windings 2G and 28 disposed on two of the poles andself-sustaining or exciting field windings 30 and 32 which are sodivided and positioned on all of the poles that the flux distribution ofthe self -excitation is symmetrical.

The field windings 30 are connected in series I in the load circuit,whereas the field windings 32 are connected in shunt across the loadcircuit for the exciter generator 22, a calibrating resistance 3i beingconnected in series with the shunt fields. The series and shunt fieldwindings of the exciter generator 22 may be cumulative with the seriesfield windings 30 providing slightly less than required sustaining fieldstrength and the shunt field 32 being only strong enough for adjustingto full self-excitation field strength to compensate for manufacturingdifferences and installation adjustment or the like. On the other hand,the shunt field windings 32 may be wound to oppose the series fieldwindings 30 where the windings 3!] supply slightly more than requiredsustaining field strength.

The series tuned exciter generator 22 is also provided with a controlfield winding 34 so wound as to provide equal windings on two of thepoles to increase the strength of one while decreasing the strength ofthe other when energized, to distort the flux distribution in the fieldstructure ina degree depending upon the energization of the controlfield winding. By utilizing the control field winding 34 in the excitergenerator 22, the plurality of field windings cooperate in the singlemachine, as disclosed in the Harding et a1. application Serial No.607,440, identified hereinbeforeto give an extremely sensitive and quickresponse of generated voltage to changes of a comparatively weak inputvoltage while at the same time giving a high amplification ratio.

The control field winding 34 which is disposed to be normallydeenergized when the generator I0 is operating to maintain apredetermined line voltage and to be directionally energized as the linevoltage increases or decreases from the predetermined value underautomatic regulation as described hereinafter to so control the excitergenerator 22' as to correct the excitation of the generator in tocorrect for such departure and maintain the line voltage substantiallyat the predetermined value.

As illustrated, the control field winding 24 is disposed to be connectedthrough segments 38, 38, 40 and 42 of a controller 44, a voltagereference network 46 and a frequency compensating means 48 to besupplied by the line voltage, a network 50 being utilized to derive apositive sequence component of the line voltage for supplying a measureof the line voltage.

The network 50 for' deriving the positive sequence component of the linevoltage is disclosed Briefly, the network comprises the potential.

transformer 52 for deriving a single phase of the three-phase linevoltage having no zero-se- Y and series-connected smoothing reactors.

quence voltage-component and current transformers 54 and 56 which causeline current to pass through the impedance in the network in such amanner as to produce a voltage drop substantially corresponding to thenegative-sequence line-voltage, and the voltage drop thus resulting issubtracted from the single phase of the line voltage to producesubstantially the positive-sequence component of the line voltage. Otherembodiments of the positive-sequence component network 50 are disclosedand claimed in the aforementioned application Serial No. 560,299, andmay be employed instead of the specific network 50 illustrated in thedrawing.

An adjustable resistor 58 is connected in the output circuit from. thenetwork 50 for providing a voltage adjusting means. The frequencycompensating means 48 may be any suitable arrangement of capacitors andinductance apparatus for accomplishing the purpose of compensating forfrequency. As will be appreciated, in many cases the frequency of theline voltage will not fluctuate greatly, and it may not be necessary toutilize the compensating means 48, but instead the positive-sequencecomponent of the line voltage from the network 56 will be supplieddirectly to the voltage reference network 46.

The voltage reference network 46 illustrated is disclosed in detail inthe copending application Serial No. 567,256, filed December 8, 1944,now

Patent 2,428,566, issued October 7, 1947, of E. L.

Harder et a1. and briefly comprises a non-linear impedance circuit 60and a linear impedance circuit 62 connected to be simultaneouslyenergized in accordance with the line voltage, and in particular, by thepositive-sequence component of the line voltage. The non-linearimpedance circuit 60 and the linear impedance circuit 62 are connectedthrough insulating transformers across dry-type rectifying units 64 and66, respectively, the output terminals of the rectifying units. be-

ing connected in series circuit relation with each other throughsuitable series-connected resistors The control field winding 34 of theexciter 22 is disposed to be connected through segments 35 and 36 acrossthe direct-current series circuit connecting the rectifying units atpoints 65 and 61, respectively, which for the predetermined line voltageare at zero potential. The elements of the non-linear impedance circuit69 and of the linear impedance circuit 62 have intersecting impedancecharacteristics and, as the line voltage fluctuates from thepredetermined value, the current drawn by the circuits varies with theresult that an unbalanced condition between the output of the rectifyingunits occurs and the control field winding 34 is energized in one or theother directions, depending upon the direction of the unbalancedcondition.

The controller 44 is also provided with segments 88, l0, l2 and 14disposed to be actuated to a circult closing position when segments 36,38, 48 and 42 are actuated to a. circuit opening position, to connectthe control field winding 34 to a manual control circuit I6 fordirectionally controlling the energizationof the control field winding34. In this instance, the control circuit 16 comprises two parallelcircuits connected between common terminals 18 and 80, one of theparallel circuits consisting of a resistor 82 having an intermediateadjustable tap 84 and the otherof the parallel circuits consisting of aresistor 86 and a pair of opposed rectifiers 88 and 89 of the dry typesuch as copper oxide rectifiers, the rectifiers being in parallelcircuit relation with the resistor 86 with the fixed tap 80therebetween. The common terminals or taps l8 and 80 are disposed to beconnected by segments 12 and 14, respectively, across the output of theexciter generator 22 when the control field winding 34 is connectedthrough segments 68 and 18 to the fixed tap 98 and the adjustable tap84, respectively.

For the purpose of better understanding the operation of the manualcontrol as will be described hereinafter, the dry type rectifiers 88 and89 may be considered as batteries in that the forward potential dropacross each of the units is substantially constant when the current fiowtherethrough changes, and each of the rectifiers may be considered as asubstantially constant potential device when the connections are suchthat the current flows therethrough. It is to be noted that with themanual control circuit connected across the exciter generator 22, thatonly one of the rectifiers 88 and 89 is active in permitting the fiow ofcurrent therethrough depending upon the polarity of the excitergenerator 22, the inactive rectifier functioning as an infiniteresistance or open circuit that does not in any way disturb or interferewith the operation of the manual control circuit for that particularpolarity of the exciter generator 22. v

In operation, with the controller 44 in the position illustrated, andassuming that the generator l0 and series tuned exciter generator 22 arebeing driven by some suitable means (not shown) for supplying power at aconstant voltage to a.

load (not shown) and that the polarity of the The non-linear impedancecircuit 68 and the linear impedance circuit 62 are so selected that whenthe positive-sequence component of the predetermined line voltage isimpressed upon the network 46, the circuits 68 and 62 have intersectingimpedance characteristics and the voltcomponent delivered to the network46 is increased, with the result that the non-linear impedance circuit60 draws more current than the linear impedance circuit 62 and theoutput voltages across the rectifying units 64 and 66 are unbalanced.With such an unbalanced condition, the larger potential across therectifying unit 64 effects a voltage drop across the control fieldwinding 34 in a direction to produce an action to oppose the excitationof the field windings 38 and 32 to decrease the output of the excitergenerator 22 to decrease the excitation of the generator in to returnthe line voltage to the predetermined value.

If the change in the line voltage is adecrease, then the linearimpedance circuit 62' draws more current than the non linear impedancecircuit 60 and the network is unbalanced to effect a voltage drop acrossthe control field winding 34 in a direction to produce an action to aidthe field windings 30 and 32 to increase the excitation of the excitergenerator 22 and thereby efiect an increase in the excitation of thegenerator ID to maintain the line voltage at its predetermined value.

In many industrial and commercial applications, it is required that amanual control be utilized for a part of the regulating action insteadof the automatic regulating operation just described. In such case, thecontroller 44 is actuated to move segments 36, 38, 40 and 42 to an opencircuit position to disconnect the control field winding 34 from thenetwork 46 to actuate segments 68,10, 12 and 74 to circuit closingposition to connect the control field winding 34 to taps 84 and 90 andthe manual control circuit 16 across the exciter generator 22. Theadjustable tap 84 is adjusted to a predetermined position whereby thevoltage drop across the section of resistor 82 connected between taps 84and equals the voltage drop across the constant potential device 88between taps and 80 when the generator I0 is operated to maintain thepredetermined line voltage and consequently, with the field windings 30and 32 supplying suilicient excitation for the exciter generator 22 tomaintain line voltage, the field current in control field winding 34 iszero. Under such conditions with the polarity of the exciter generator22 as indicated, current flows through only rectifier 88 of the opposedrectifiers as the rectifier 89 effectively blocks the flow of current.

In operation, if the voltage of exciter generator 22 tends to rise forany reason, the voltage across the section of resistor 82 connectedbetween taps 84 and 80 also rises whereas the voltage across therectifier 88 connected between taps 98 and 80 remains substantiallconstant. Under such conditions, the potential at tap 84 rises withrespect to the potential at tap 98 and current fiows from the tap 84through segment 10, control field winding 34 and segment 68 to tap 90whereby the excitation effect of winding 34 is in opposition to theexcitation effect of windings 30 and 32 to reduce the voltage of theexciter generator 22 to its original value at which value, balance inthe manual control circuit 16 is again restored and the current flowthrough the control field winding. 34 is reduced to zero.

If the voltage of exciter generator 22 tends to decrease, then thepotential at tap 90 is'large with respect to the potential at adjustabletap 84 and the fiow of current in the control field winding 34 isreversed whereby the directional efiect of the energization of winding34 aids the excitation effect on the exciter generator 22 by reason ofwindings 3i! and 32 to increase the excitation of exciter generator torestore the balance of the control circuit 16 thereby effect thedeenergization ofcontrol field winding 34.

The foregoing operation is that encountered for a normal operation ofthe system with the polarity of the exciter generator 22 as indicated,and in which operation. the rectifier 89 of the manual control circuitit has no part. However, in certain industrial applications, such aswhere a plurality of the generators W are connected in parallel, acondition is sometimes encountered wherein the polarity of the excitergenerator 22 is reversed from that indicated. For example, if thegenerator system (not shown) which is connected in parallel with thegenerator ill, illustrated, should fail in such a manner as to drive itsexcitation very high, a high voltage is encountered across loadconductors i6, i8 and El).

Assuming that the controller 44 is in the position lllustratedforautomatic regulation, it is apparent that the network it is responsiveto variations from a given condition on the load circuit, and that theresulting unbalance between the output voltages across the rectifyingunits 64 and 66 of the network 46 caused by the high voltage conditionreferred to, is such as to effect an energization of control fieldwinding 34 in a direction to produce an action to oppose the excitationof the field windings so and 32 of exciter generator 22 to decrease theexcitation of generator l0. However, because of the failure of the othergenerator system, such reduction in the excitation of generator it failsto correct the high-voltage condition on the load conductors i6, i8 and2t, and the automatic network 46 continues to so effect the energizationof control field winding 34 that the output of the exciter generator 22actually reverses polarity and, at the same time, the excitation offield winding i4 passes through zero and becomes of opposite polarity.Under such conditions, it is quite apparent that the generator ill mayslip a pole relative to the generator (not shown) with which it isconnected in parallel.

As long as the system is connected on automatic regulation, the networkGt continues to be responsive to the high-voltage condition onconductors l6, l8 and to to cause a flow of current in the control fieldwinding Sill to normally produce an action to oppose the excitation offield windings 3t and for the polarity shown. How- 'ever, since thepolarity of the exciter generator 22 has been reversed, the resultingexcitation of control field winding 36 actually produces an action toaid the field windings all and 32 to increase the output of the excitergenerator 22 and so increase the excitation of the generator ill as toeiiect a rise in the generator voltage to its electrical ceiling.

When the condition just described arises, it can be quickly corrected byoperating the controller id to disconnect the network (iii from thecontrol field winding 36 and to connect the manual control circuit iiiin circuit between the exciter generator 22 and the control fieldwinding 36. Assuming that the controller is not operated until after thepolarity of the exciter generator 22 is reversed from that shown, thecurrent flow through the manual control circuit i6 is then reversedflowing from terminal to to terminal ill with the rectifier 38 active inthe circuit and the 22 to its original value and opposed rectifier 88functioning to block the flow of current therethrough. Thus without therectifler 89 connected in the circuit as illustrated, the manual controlcircuit 16 would be inoperative under the condition described to controlthe operation of the exciter generator 22 and consequently theexcitation of the generator in.

With the polarity of the exciter generator 22 reversed from the polarityillustrated and the manual control circuit it connected as described, itis-seen that the potential at the adjustable tap 84 is more negativethan the potential at the fixed tap 9D with the result that currentflows from the rectifier 89 through segment 68, control field winding 34and segment ill to the adjustable tap 84 in a direction to normallyboost the excitation of exciter generator 22 under normal polarityconditions. However, as the polarity of the exciter generator 22 isreversed and the excitation of the windings 3E] and 32 is reversed, suchexcitation effect of the control field winding 84 actually produces anaction to oppose the effect of the windings so and 32 to effect a.decrease in the output of the exciter generator 22 and there by sodecrease the excitation of generator I0 as to eiiectively lower itsvoltage from its electrical ceiling. By adjusting the tap 84 in adirection toward the common terminal '18, the potential at tap 84becomes more negative with respect to the potential at tap 90, so thatthe current flow through control field winding 34 can be quicklycontrolled to regulate the exciter generator 22 to supply onlysufiicient excitation of the generator it as to maintain the outputtherefrom at a predetermined regulated value.

The regulating system should not again be connected for automaticregulation until the generator in is disconnected from the parallelcircuit relation with the other generators, and this operation can beperformed substantially simultaneously with the operation of controller44 at the time of connecting the manual control circuit 76 in circuitwith the exciter generator 22 and control field winding 34.

During the course of the initial reversal of polarity of the excitergenerator 22, it is to be noted that the excitation of generator in alsopasses through zero and also reverses. If the manual control circuit "i6has been operated to control the excitation of generator in to lower itsoutput from the electrical ceiling to a predetermined normal regulatedgenerator voltage, then when the controller 44 is again operated todisconnect the manual control circuit '56 and connect the system forautomatic regulation, the network 35 should function to maintain thepredetermined regulated enerator voltage.

However, it is to be noted that the exciter generator 22 is still ofreversed polarity so that if the output of generator ill is above itsregulated value, the network it functions to effect a flow of current inthe control field winding 34 in a direction to produce an action tonormally oppose the excitation of windings 3t] and but which actuallyaids the excitation of windings Eli and 3 2 when the polarity of theexciter generator is reversed and if permitted to thus operate, it veryquickly so excites the generator it as to drive it to its electricalceiling. Therefore, before the system is changed from manual control toautomatic control. the tap 86 should be so adjusted as to maintain theoutput of generator it slightly below the predetermined regulatedgenera-tor volt- 4 age, so that when the system is connected forautomatic regulation the nework d6 responds to such output to effect aflow of current in the control field winding 34 in a direction toproduce an action to normally aid the excitation of windings 30 and 32under normal polarity conditions for the exciter 22. c

As the polarity of exciter generator 22 is still reversed, theexcitation of control field winding 34 just described actually producesan action to oppose the effect of windings 30 and 32 and continues tooppose them until the excitation of the exciter generator 22 passesthrough zero and the polarity of generator 22 returns to normalpolarity, as indicated, after which the excitation of winding 34produces an action to aid the windings an and 32 to so excite theexciter generator 22 that its output is suificient to provide normalexcitation for the generator l0. As the output of the generator inapproaches its normal regulated value, having passed through zero withthe change in polarity cf the exciter generator 22, the network 46functions to decrease the current flow through the control field winding34 until it is zero at the normal regulated value of output for thegenerator Hi. The network 46 then responds to changes in the output ofgenerator ill to automatically control the excitation of the excitergenerator 22 to maintain the normal regulated output of the generatorIll, as described hereinbefore. Where desired the generator l may againbe synchronized and connected in parallel circuit relation with othergenerators (not shown) in a manner well known to the industry.

A desirable function of the manual control circuit 16 will beappreciated when the operation of the exciter generator 22 is consideredwithout the control circuit 16 being connected to respond to the voltageof the exciter 22. For example, with the manual control circuit 16disconnected from the exciter generator 22, if a reactive load or ashort circuit is suddenly applied to the generator H), such loads areaccompanied by a transient increase in current flowing in the fieldwinding 14 which, in turn, causes a transient increase in the currentflowing in the series field winding 30 of exciter 22. If the transientfield current in field windings 30 and i4 could be maintained at theirinitial values,'steady operation of the generator Iii under the loadwould be obtained and the short-circuit current would be maintained atthe transient value instead of reducing it to its lower synchronousvalue.

Under such conditions, the exciter generator 22 in effect tends tosustain the high transient value of field current regardless of thepolarity of the exciter generator 22. This is evident for the transientcurrent flowing through the series field winding 30 tends to effect anincrease in the voltage output of exciter 22 to increase the excitationof the generator l0 and thereby tend to maintain the field current ofthe generator ID at its transient value with the polarity of the excitergenerator 22 as shown. If the manual control circuit 76 is connectedacross the exciter generator 22 as described hereinbefore, the increasethus resulting in the excitation of exciter the polarity of excitergenerator 22 is reversed from that indicated, the increase resulting inthe excitation of exciter 22 by reason of the transient current rendersthe potential of the tap 84 more the excitation of the windings 3D and32 for nor- 22 by reason of the transient current effects a change in.the potential drop across the section of resistor 82 between taps 84 and80 whereby current flows in the control field winding 34 to produce anaction to oppose the excitation eifect mal polarity of the excitergenerator 22 but since the polarity is reversed, the excitation of thewinding 34 actually produces an action to oppose the excitation ofwindings 30 and 32 to again cause a slow drift of the voltage of excitergenerator 22 to its original predetermined value. The operation of themanual control circuit 16 just described is of sufll-cient duration topermit short circuits on the line conductors l6, l8 and 20 for asufficiently sustained period that circuit breaker (not shown)coordination can be obtained. At the same time that the action of thetransient current is taking place, there is also a changein the voltageacross the generator in and as will be apparent, the normal regulatingaction of the manual control circuit 16 is also of such duration that amanual adjustment of the circuit 16 can be had to correct the voltagebefore the change from transient to synchronous voltage can be correctedautomatically.

The manual control circuit 16 utilized in this invention has anexcellent settling ability for good stability, as evidenced by the factthat when a heavy load is applied to the line conductors and then laterremoved while the manual control circuit is connected to .control theexcitation of the control field winding 34, the voltage of the generatorI0 is returned to substantially its original value. Further, as themanual control circuit 16 automatically provides a relatively smallenergization for the control field winding 34 for changes in the excitervoltage but a large forcing action when the adjustable tap 84 is movedbeyond the usual setting range, it is found that a very fast restorationof voltage can be obtained with the manual control. The fact that themanual control circuit 16 also functions regardless of the polarity ofthe exciter generator 22 to control the output thereof to maintain anormal regulated voltage on the generator in is a distinct advantage inregulating systems of the.

type described.

We claim as our invention:

1. In a regulating system for a dynamo-electric machine, in combination,an exciter for supplying the field excitation of the dynamoelectricmachine, a pair of circuits disposed to be connected in parallel circuitrelation across the exciter, one of the parallel circuits comprising aresistor having an adjustable tap, the other of the parallel circuitscomprising a resistor and a pair of parallel connected but opposed drytype rectifiers connected in series circuit relation therewith with afixed tap therebetween, and a control field winding for the exciterdisposed to be connected to the adjustable tap and the fixed tap to bedirectionally energized in accordance with the potential at theadjustable and fixed taps,

2. In a regulating system for a dynamo-electric machine disposed tosupply a load circuit, in combination, an exciter for supplying thefield excitation of the dynamo-electric machine, a control field windingfor the exciter disposed to be directionally energized to control theexcitation and polarity of the exciter, a manual control circuitdisposed to be supplied by the exciter and connected to the controlfield winding, the manual control circuit including a pair of opposeddry type rectiiiers connected in parallel circuit relation whereby thecontrol circuit is ei- Iective when the polarity of the exciter isreversed to control the directional energization of the control fieldwinding, and means disposed for operation to connect the manual controlcircuit to the exciter and control field winding.

3. In a regulating system for a dynamo-electric machine disposed tosupply a load circuit, in combination, an exciter for supplying thefield excitation of the dynamo-electric machine, a control field windingfor the exciter disposed to be directionally energized to control theexcitation and polarity of the exciter, a manual control circuitdisposed to be supplied by the exciter and connected to the controlfield winding, the manual control circuit consisting of a pair ofparallel circuits, one of the parallel circuits consisting of a resistorhaving an adjust,- able tap, the other oi the parallel circuitsconsisting of a resistor and a pair of opposed dry type rectifiersconnected in series circuit relation therewith with a fixed taptherebetvmeen, the opposed rectifiers rendering the manual controlcircuit effective when the polarity of the exciter is reversed tocontrol the directional energization of the control field winding.

4. In a regulatingsystem. for a dynamo-electric machine disposed tosupply a load circuit, in combination, an exciter for supplying thefield execitation of the dynamo-electric machine, a

control field winding for the exciter disposed to be directionallyenergized to control the excitation and polarity of the exciter, amanual control circuit disposed to be supplied by the exciter andconnected to the control field winding, the manual control circuitcomprising a pair 0! circuits disposed to be connected in parallelcircuit relation across the exciter, one of the parallel circuitscomprising a resistor having an adjustable tap, the other of theparallel circuits comprisin'g a resistor and a pair of parallelconnected but opposed dry type rectiflers connected in series circuitrelation therewith with a fixed tap therebetween, the opposed rectifiersrendering the manual control circuit effective when the polarity of theexciter is reversed to control the directional energization of thecontrol field winding, and means disposed for operation to" connect themanual control circuit to the exciter and the taps of the manual controlcircuit to the control field winding,

HOMER M. RUSTEBAKKE. ALBERT W. KIMBALL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

